Valves for Hydrogen Sulphide (H₂S — Sour Gas) Service
Hydrogen sulphide (H₂S) is a highly toxic, flammable gas encountered in crude oil and natural gas production ('sour service'), refinery amine treating, geothermal wells, biogas/landfill gas, and Claus sulphur recovery units. H₂S is immediately life-threatening at >100 ppm (IDLH); lethal at >500 ppm. Beyond toxicity, dissolved H₂S causes sulphide stress cracking (SSC) and hydrogen-induced cracking (HIC) of carbon and low-alloy steels at even very low partial pressures. NACE MR0175/ISO 15156 compliance is mandatory for all metallic valve components in sour service.
Pressure Range
1–700 barg (wellhead to processing)
Temperature
Ambient to +300°C (Claus SRU)
Industries
Upstream oil & gas (sour wellheads), Refinery sour crude service, Gas sweetening (amine treating)
Key Properties — Hydrogen Sulphide (H₂S — Sour Gas)
- IDLH: 100 ppm; lethal above 500 ppm — immediately dangerous to life and health
- SSC risk: H₂S partial pressure >0.0003 MPa (0.05 psia) triggers NACE MR0175 sour service
- HIC: hydrogen absorbed at surface causes sub-surface blister cracking in plate/pipe steels
- SOHIC (stress-oriented HIC): combined effect of hydrogen + welding residual stress
- Flammable: 4–44% in air — ATEX Zone 1 in production areas
Material Compatibility — Hydrogen Sulphide (H₂S — Sour Gas)
Ratings are indicative. Actual compatibility depends on concentration, temperature, velocity, and presence of contaminants. Always consult corrosion tables or a materials engineer.
| Material | Rating | Notes |
|---|---|---|
| NACE MR0175 qualified WCB (hardness controlled) | Excellent | Mandatory — Brinell hardness ≤200 HBW, Rockwell C ≤22 HRC, CE ≤0.43 per NACE MR0175. |
| SS 316L (NACE qualified) | Good | Acceptable for most H₂S service; use low-carbon grades, verify with NACE MR0175 SSC zone. |
| Duplex 2205 (NACE qualified) | Good | Restricted to solution-annealed condition, max hardness per NACE MR0175 Table D.1. |
| Inconel 625 (UNS N06625) | Excellent | Excellent SSC resistance; used for valve trim and high-alloy applications. |
| Standard carbon steel (uncontrolled hardness) | Not Recommended | SSC failure risk — mandatory to verify NACE compliance. |
Recommended Valves
Ball Valve (NACE MR0175, WCB body, Inconel trim)
Standard isolation for sour gas, crude oil, and multiphase hydrocarbon pipelines
Gate Valve (NACE, API 600)
Full-bore sour gas line isolation; through-conduit slab gate for pipeline service
Globe Valve (NACE, Stellite trim)
Control service in sour service amine treating and gas sweetening plants
Check Valve (dual plate, NACE MR0175)
Compressor and pump protection in sour service
ESD Ball Valve (NACE, fire-safe, SIL rated)
Emergency shutdown for wellheads and sour gas processing
Valves to Avoid
Any valve with hardness >200 HBW body or >22 HRC trim without NACE MR0175 qualification
Chrome-plated stems in H₂S service — plating creates galvanic cell
Special Considerations
Applicable Standards
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